There are numerous instances where it is desirable to distribute signals within a relatively local area such as a building or series of buildings. A particular application is the distribution of video signals. For example, a school may have a number of classrooms or administrative offices, each having a television monitor, and it may be desired at a given time to provide a program to all the classrooms and offices, originating either from a source within one of the classrooms or offices, such as a VCR, or from an outside source such as a local cable system. A system capable of distributing wideband signals is necessary to provide these programs to the desired locations. Similarly, a corporation may have a building, or several closely spaced buildings, with numerous conference rooms equipped with television monitors and analogous program presentations may be desired.
An example of such a wideband distribution system is disclosed in International Publication Number WO 97/01931, titled "Wideband Signal Distribution System", which is assigned to the assignee hereof and is incorporated herein by reference. That Publication disclosed a wideband distribution system utilizing existing twisted pair cable which is typically installed in buildings for telephone communications. The system, therefore, would require no additional wiring to provide the wideband distribution system to an existing building. This system utilizes distribution units which can be cascaded in order to reach many rooms in the building which are connected to the telephone wiring system. Each distribution unit has a plurality of inputs and outputs, each of which is connected to a different room outlet. In order to reach additional rooms, another distribution unit is simply cascaded into the system. Any of the rooms connected to a distribution unit can be utilized either to transmit a source signal to the entire building or as a receiving location to receive any signal which is transmitted over the distribution system from another location. Since each outlet in this system is capable of both input and output, signals can be distributed to any location from any location. Signals at the input location are generated by a base band signal source and are modulated to a desired frequency channel.
A problem exists, however, when it is desirable to distribute wideband modulated signals to many classrooms or locations. As the number of classrooms increases the number of input and output locations increases, and the amount of near end cross talk also increases. This is due to increased length of cable in the system necessary to support the increased number of classrooms. Near end cross talk occurs as a result of capacitive coupling of signals between the input wires and output wires of each cable. It is therefore an object of this invention to reduce near end cross talk in a broadband distribution system having many input and output ports.
Another problem exists when many outlets are present in the distribution system in that the distance between each distribution unit and outlet is variable. Outlets which are farther from the distribution unit will necessarily contain longer lengths of cable between the distribution unit and the outlet. This results in signal attenuation levels at each outlet being different based on the distance each outlet is from the distribution unit. It is therefore an object of this invention to provide a circuit which simulates long and short lengths of cable in order to provide consistent system signal attenuation levels at each outlet.